1. Field of the Invention
Many prior art silicate materials have been described in the prior art. Among those described previously are naturally occurring alkali and alkaline earth metal silicates. Additionally, sodium, aluminum and calcium silicate materials have been prepared by a variety of methods including the reaction of sodium silicate with calcium chloride.
2. Description of the Art
The invention relates to a process for the production of calcium hydrosilicate bonded shaped articles, wherein a crude mixture is formed from quartz powder and, if appropriate, a thermally activatable setting accelerator, a pore-forming agent and water and, if appropriate, other additives, the crude mixture is shaped into blanks and the blanks are autoclaved after reaching a sufficient rigidity.
A process of this type is described in U.S. Pat. Nos. 4,376,086 and Re. 32,673, which description is incorporated by reference herein. These patents describe a process wherein a crude mixture is formed from: SiO.sub.2 -containing powder (e.g., quartz powder and/or fly ash); slaked lime; a thermally activatable setting accelerator (e.g., alumina cement, citric acid anhydrite, hydrated and anhydrous calcium sulphate); Portland cement; a pore-forming agent (e.g., a foam); water; and, if desired, other additives. The crude mixture is shaped into a strand in a continuous strand molding device under the action of heat, and the rigidified strand leaving the continuous strand molding device is cut into inherently stable blanks, which are autoclaved. The pore-forming agents include preprepared foams, for example, those based on protein, with which the crude mixture is rendered porous. This procedure makes it possible to produce lightweight sand-lime bricks and other sand-lime shaped articles having low bulk densities of e.g., 400 to 1000 kg/m.sup.3, very high compressive strengths of up to 25 N/mm.sup..sup.2, excellent thermal insulation properties, low shrinkage and creep values, and a low capillary water absorption capacity. Further, the shaped articles can be sawed through as needed.
It is also known to produce shaped articles of foam concrete by a similar procedure in which a quartz powder is mixed with Portland cement, unslaked lime, water and a pore-forming agent (e.g., A1 powder) or a preprepared foam, and the resulting crude mixture is poured into a mould. When the crude mixture is sufficiently rigid, it is cut into blanks in the vertical and horizontal direction and these blanks are then autoclaved. This concrete lank procedure also allows production of shaped articles with low bulk densities, high compressive strengths and excellent thermal insulation properties. Further, these shaped articles can be sawed through as needed.
In the paper industry, waste paper is collected and processed into recycled paper. Recycled paper in turn becomes waste paper, which when processed for recycling leaves material in a waste paper slurry which because of its short fiber length is no longer suitable for the manufacture of recycled paper and has therefore been a waste product to be incinerated or dumped.
Although it is known to use cellulose fibers (e.g., Kraft cellulose, used inter alia as an asbestos substitute) in products such as fiber boards bound with plaster, cement or calcium silicate, for instance in cladding panels (see, e.g., German patent application A-2 832 125), this is not a case of utilizing scrap materials. Rather, products having certain properties such as increased flexural strengths utilize the reinforcing properties of wood fibers which requires a process of incorporating fibers of a minimum fiber length which a waste paper pulper slurry remaining after repeated recycling does not contain. This waste paper pulper slurry is totally unsuitable for such a purpose. For the long cellulose fiber containing products, the raw material is shaped into boards or blocks by means of presses or winding machines in order to attain a good product strength and to reduce the porosity.
For the production of porous articles a pore-forming agent is used. It is known in the art to use a pre-formed foam to be mixed with a raw mixture containing the other concrete ingredients or to use a foaming agent to be mixed with a raw mixture which is then stirred for foaming or to use a gas pores forming agent (Al powder) which upon reaction with calcium hydroxide produce H.sub.2 filled pores within the raw mixture.
In the production of paper, wood is disintegrated into fibers which normally range in length between 0.1 to 1 cm or more (up to several cm) which afterwards are present in the paper. If waste paper is disintegrated into its fibers, a certain amount of these fibers are destroyed, i.e., these fibers are reduced to fiber constituents or fiber fragments, which are so small that they can no longer be used for the paper production. These fragments have a length generally smaller than 1 mm. These short fiber fragments are collected as a slurry which normally is a waste product which is incinerated or dumped. The slurry generally has a solids content of about 5 to 15 weight %; however, the cellulosic fiber fragments of the slurry can be swelled as needed by the addition of water to achieve this solid content.
These swelled fiber fragments are uniformly mixed with the other ingredients of the raw mixture from which blanks are formed which are autoclaved to obtain the final products. Within the raw mixture, the fiber fragments form pores consisting substantially of water and of somewhat solid material (swollen cellulose). Within the dried final product the water of the pores is practically eliminated and only the solid content remains. The use of small cellulosic fiber fragments leads to fine pores which are distributed very uniformly within the article. The fine pores formed produce concrete with good structural strength and mechanical properties. The use of cellulosic fiber fragments leads to fine pores which are distributed very uniformly within the article. The fine pores which are distributed very uniformly within the article. The fine pores which are distributed very uniformly within the article. The fine pores formed produced concrete with good structural strength and mechanical properties.
It is an object of the present invention to provide a process which makes it possible to utilize cellulose fiber containing scrap materials in the production of construction materials and to provide uniformly distributed fine pores in concrete products to effect good structural strength and mechanical properties.
This object is achieved by using as the pore-forming agent waste paper slurry consisting of short length cellulosic fibers or fiber constituents, which have been digested in a pulper.
The inventor has discovered that waste paper slurry prepared in a pulper, which contains fibers too short to be used as reinforcing fibers in products including recycled paper, is useful for rendering porous a crude mixture from which calcium hydrosilicate bonded shaped articles can be formed. Additionally, the invention allows advantageous use of materials previously discarded so as to not create environmental problems.
Further, the process of the claimed invention results in a product having very fine "microscopic" pores which can be formed into shaped articles that can be sawed up, can advantageously be nailed, and can be fastened with screws.